1. Field of the Invention
The invention relates generally to a device for removal of electrical components and more particularly to a device for desoldering and removing surface mount devices from a circuit board without damaging the circuit board.
2. Description of the Related Art
Surface mount devices include various electronic circuit components having electrical leads protruding from the sides which are attached to printed circuit boards by either solder or conductive adhesive. One type of leads extend straight down from the chip and form a butt joint with the circuit board. Other leads, referred to as gull wing leads extend down from the chip to the board and then extend outward a short distance along the board where they are joined to the board by solder. Still other leads, referred to as J-shaped leads extend down from the chip and curl underneath the chip where they are soldered to the circuit board. Surface mount devices having J-shaped leads are commercially manufactured having dimensional tolerances which are quite large, on the order of 0.01 inches. Therefore, the position of the J-shaped leads relative to one another may vary substantially in chips of the same size and type.
When a surface mount device is found to be faulty or malfunctioning, the component is removed from the circuit board by heating each of the solder connections above its melting temperature. Several methods are available for heating the solder including non-contact heating with a hot gas or infrared lamps, and direct contact heating with special heated tools having tips size to match the individual components. The non-contact methods of heating are typically useful only for repetitive component removal due to the long setup time required to establish the proper operating parameters for these methods.
Contact heating devices are generally useful for removing a few components from a circuit board as the need arises. These contact heating devices generally utilize fixed size contact elements which are configured to contact all of the leads of a particular size chip and are heated via conduction through a conductive stem. The relative large mass of these contact elements prevents rapid heating of the device to operating temperature. Examples of such contact heating devices having fixed size contact elements are disclosed in U.S. Pat. Nos. 3,632,036 and 3,579,795.
Due to the above-described large tolerances in surface mount components having J-shaped leads, the fixed size contact elements must be made to accommodate the largest possible component size within the tolerance allowance. This tolerance allowance causes the contact element to be too large for most components. When the tool tip is too large for a particular component, the contact surfaces do not make contact with all of the leads, whereby some of the soldered connections are not melted. Many circuit boards have been destroyed when trying to remove a component from the board when all the soldered connections have not been melted.
In an attempt to solve this problem, component removal has been conducted with either fixed size removal devices which utilize molten solder or removal devices having a set of movable contact blocks which are moved to contact the leads of the component. In the molten solder type device, grooves are provided in the contact portion of the removal device for molten solder which is used to fill the gaps between the leads of the component and the oversized removal device. The drawback of this device is that the molten solder does not flow into all the grooves in a consistent fashion. When the solder does not reach all the grooves, some of the leads are not contacted, preventing the solder connection from being melted and causing damage to the circuit board.
The grasping type removal devices are provided with grasping contact surfaces which are manually moved to accommodate differences in component size. Examples of grasping type removal devices are shown in U.S. Pat. Nos. 4,034,202 and 3,895,214. These grasping type devices require operator experience and technique to properly align the grasping contact edges with the component leads without damaging the circuit board or surrounding components. Damage to the board can also occur if an attempt is made to remove the component before all the connections are melted.